I worked in a daycare for 4 years and learned quite a few different activities that kids of all ages enjoy. One of them was playing with cool whip (or for older kids, shaving cream). We used to do this once a week in the toddler room.
I bought some to make a cake for my mom's birthday and ended up leaving it on the table for like 4 hours. I was so annoyed it was ruined because of my inability to remember things these days but instead of throwing it away I decided the kids could play with it the next day and I wouldn't feel like it was completely wasted.
Disclaimer: if you plan on doing this activity with kids who aren't in high chairs, outside is the best place so you can hose everything off. Make sure the kids either wear art smocks or old clothing because it will inevitably have shaving cream all over it. I found colored whipped cream everywhere when I was cleaning and even had to scrub parts of my carpet. Who puts carpet in a dining area anyways, stupid apartments, makes no sense to me.
This activity was a simple one and the kids loved it. They were busy making drawings, smearing, and slapping the cool whip for a good 30-45minutes. $1.50 (less if your store actually has the offbrand in stock) for nearly an hour of entertainment for 2 kids....not bad.